Revetment and block therefor



March 14, 1944. 1.. F. HARZA REVETMENT AND BLOCKS THEREFOR Filed June30, 1 939 INVENTOR: I

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Patented Mar. 14, 1944 UNITED PATENT OFFICE 3 Claims.

This invention relates in general to new and improved blocks adapted tobe combined and used to provide a protective cover or revetment forsurfaces and embankments, particularly of streams, dams, and the like.

In protecting river banks against scour for high velocity current, or inprotecting the upstream slope of an earth dike, levee, or embankment, orfor shore or beach protection against waves, it is customary to use,among other means of protection, a so-called riprap consisting ofnatural and irregular blocks of stone, either hand laid and with crackschinked up to form a rough eifect of paving, or loose dumped, as thecase may be.

In either case it is customary and necessary to provide a layer ofcrushed stone or gravel underneath the riprap, particularly whereprotection is required, because waves rolling up the face of the riprapwill cause a high velocity of water in the spaces between the stonesupon its return down the slope, and will scour sand, dirt or clay fromunderneath the riprap stones causing them to settle into the fill. Theriprap must, therefore, be laid on a surface of crushed stone or gravelwhich is able to resist scour from the current which will exist in thespaces underneath and between the stones,

The use of natural riprap necessarily produces irregular spaces betweenthe stones, with consequent high velocity of the receding water throughspaces between the stones, sometimes resulting in local scour even Wheregravel or crushed stone is used beneath the riprap. The fact thatnatural stones are of all sizes and shapes necessitates a "great amountof careful selection and placing of each stone and much chinking toavoid the above result. v j

Smooth concrete slabs have been used for many years for bank protectionbut in general they have produced a very unsatisfactory result. Mostconcrete slab faces used on earth dams or for other slope protectionhave been provided with expansion joints to allow for temperatureexpansion and contraction and these joints are a source of trouble. Whena Wave rolls up the face of such a protected embankment water will enterthese joints and finds its way underneath the slabs, or units of slabs,and unless the water can flow out more freely than it flowed in, it Willbuild up a hydrostatic pressure tending to lift the slab.

It is also true that rain water falling on top of an embankmentprotected by. a concrete slab will often seep into the material andaccumulate underneath the slab to an elevation higher than the elevationof water in the reservoir, thus producing an up-lifting hydrostaticpressure behind the slab. Since it is necessary for a slab to lie fiatand in close contact with the earth embankment upon which it is built,it requires only a very small amount of water to fill the pores of thematerial, or any thin film or clearance which may exist beneath theslab, and thus produce hydrostatic pressure. Since concrete weighs about2A times the weight of water it is necessary only for the materialbeneath the slab to become saturated to a height of 2.4 feet above theelevation of water in the reservoir in order to have lifting efiectenough to raise a concrete slab one foot thick,

The result has been that many if not most concrete slabs for waveprotection have been destroyed by uplift and the slabs have been liftedoff and slid down the face of the dam to the bottom of the reservoir.This has happened in so many cases that such construction is notconsidered correct and is not now recommended or used.

Small unit paving blocks on the face of an earth embankment avoid theobjections and difficulties described for large concrete paving slabs.Any water which enters the joints or clearances between the blocks intothe gravel or earth beneath them, cannot build up enough head to liftthe block because of the freedom of escape of the Water at any jointbetween the blocks. In other words the water will escape as freely as itentered and cannot accumulate to a height above the height of water inthe reservoir nor raise the blocks from their predetermined place.

It is recognized that a rough surface on the slope of a dam will assistin breaking up the waves and in preventing them from rolling as far upthe slope as they would on a smooth surface such as a concrete slab. Theexperiment has been made of setting concrete tetrahedrons on the slopingface of a dam or river bank, their bases serving to cover the entiresurface, but this experiment was not attended with success. Atetrahedron is so high in comparison with its base, width, and area thatit is unstable and subject to being tipped over by a heavy blow from awave or from driftwood which is pounded against the face of a slope bythe Waves. Moreover a true tetrahedron has no thickness of base and itis necessary for the edges to match and meet each other accurately inorder to protect the entire surface. As the edges are thin, any slightinequalities in the bed of gravel underneath them will raisethe edge ofone tetrahedron slightly above the other, leaving an opening underneathfor the entrance of high velocity water, causing it to scour the gravelfrom beneath the higher tetrahedron. It has therefore been proven to benecessary for successful application, that the pyramidal unit be lowerin height in comparison with base width than a tetrahedron in order tobe stable, and also that it should have a suiiicient thickness of basein the form of a, prism having the same base area as the unit, and withessentially parallel sides several inches thick so that any inequalitiesin the surface of the gravel bed beneath the concrete units will notcause one block to be lifted higher than another to such an extent as toexpose to the high current and wave action the gravel underneath thehigher block.

The present invention therefore has a number of important objects, amongwhich are the following:

To provide a new and improved form of block; to provide a new andimproved revetment made of the block; to prevent accessibility of waterto the bed or layer below the blocks; to prevent the formation of directchannels or passageways between the blocks; to obviate the necessity ofaccurately aligning or leveling blocks on their bases; to provide meansfor locating blocks in adjacent courses; and in general to produce a newand improved revetment by the use and combination of the blocks hereinshown and described.

Other and further objects of the invention will appear hereinafter, theaccompanying drawing illustrating the preferred construction, shapes andcombinations of blocks to produce a protective cover or revetment, inwhich Fig. 1 is a perspective of a pyramidal block in accordance withthis invention;

Figs. 2 and 3 are top and side views respectively of a triangularpyramidal block;

Fig. 4 is a top view of a hexagonal block;

Fig. 5 is a view illustrating the application of blocks of the typeshown in Fig. 1 to an inclined revetment surface;

Fig. 6 illustrates a means for interlocking triangular blocks incourses;

Fig. '7 illustrates the location of pyramidal blocks in staggeredcourses to prevent the formation of continuous channels between them;and

Fig. 8 illustrates the objectionable location of pyramidal blocks insuccessive courses which provide a continuous scouring channel.

In this type of revetment blocks, to make them safe from overturning, itis evident that the force against any of the faces of the pyramidscaused by the blow of a wave or of driftwood, should have a directionwhich would fall within the base of the unit. For this to be true anyface of the pyramid must ehave an angle substantially ninety degrees ormore with the opposite edge or side of the pyramid. Pyramids could be ofany base shape which will fit readily into a complete pattern to coverthe entire area and the most convenient shapes for this purpose aretriangular, square, rectangular, or hexagonal.

Referring now more particularly to the drawing, Fig. 1 shows aquadralateral prismatic base l8 with a superposed pyramidal structure Hof equal sides having an apex in which the opposite I by any edge withthe opposite side face is substantially ninety degrees.

In Fig. 4 is shown a top view of a hexagonal block with a similarprismatic base I4 of uniform thickness as in Fig. 1, surmounted by ahexagonal structure l5 in which opposite faces are substantially atright angles to each other.

In Fig. 5 is shown a portion of an inclined bank it covered with agravel bed H which may be of graduated thickness and this bed surmountedby a plurality of revetment blocks IE! arranged in succeeding coursesand spaced close together so that there are no substantial spacesbetween the blocks even though there is some difference in elevation ofthe gravel bed which tilts some blocks with respect to the other, theprismatic bases being of sufiicient height so that the gravel bed is notexposed at any point to the direct scour of waves or returning waterpassing between the blocks.

In Fig. 6 is shown a plan of a portion of an area of slope protected bytriangular blocks having triangular bases, the point of one block'ineach course being upward and the next block in the same course beingdownward and thus alternating throughout the course. It is desirablethat the blocks in one course shall break joints with the blocks in thecourse above and below so that a wave in rolling up the face or inreturning down the face of the revetment will not have a continuouschannel to follow but will continually strike against the angular faceof one block and will be diverted around the face of that block to theadjoining channels on either side, striking the face of the blocks inthe next course in the same way and thus making its course as tortuousas possible to destroy the energy of the wave, reduce its velocity anddissipate its force.

In laying up the blocks of a true triangular pattern as shown in Figs. 2and 3, it is conceivable that the blocks of one course will graduallygain in horizontal distance over the blocks in the next upper or lowercourse, due to slight difference in sizes of the blocks, the closenesswith which they are packed, or even to the contour of the surface towhich they are applied, until the V-shaped channels would form acontinuous passage as represented by the lines a. and b in Fig. 8, whichare objectionable for the reasons above set forth.

them from forming a continuous path as in Fig. 8. Blocks of this kindand shape may be conveniently formed with the points downward in metalforms which can be packed continuously together so that concrete can bepoured from a moving concrete mixer and screeded over the surface tofill all of the forms at a correspondingly low cost. The blocks may alsobe made in concrete block machines, the forms removed and the blockscar.- ried to one side on a belt conveyor or other means for storage.

In Fig. '7 is shown a pattern of square base pyramids built and set upin staggered courses to break joints and serve the same purpose as thetriangular pyramids. This form does not readily admit of the provisionof the notch as shown in the triangular form, in order to insuredefinite positioning of each block, but othervise would be assatisfactory as the triangular base.

A similar pattern may be built up of hexagonal base pyramids set insucceeding and somewhat inter-engaging courses, as each pyramid wouldhave a definite position and the water flowing between them would have atortuous path. The forms for constructing them would be more complicatedto make and more expensive, and more skill would be required to laythese blocks correctly.

With this type of block which covers substantially the entire face ofthe wall or bank which it protects, the water even from a rapid streamor from waves is not accessible to the space beneath the blocks, thereis no scouring action which tends to remove the supporting sub-soil orgravel, there is no tendency for the blocks to become displaced, andeven the path of water up and down the face of the revetment is sotortuous that the force of the water is reduced, dispelled anddissipated.

In carrying out the method of constructing a revetment of this kind, thesurface to be protected is first provided with a layer of crushed stone,aggregate, or gravel I'I, substantially leveled on its upper or outersurface, and graduated in thickness from top to bottom if desired. Uponthis are placed the blocks which are laid in a pattern depending upontheir shape, with the bases fitting closely together, and entirelycovering the surface. The blocks are laid in courses or tiers, theblocks staggered in adjacent courses to break joints and prevent theformation of continuous hannels in successive courses.

This protects the bed or bank against erosion or scouring, the highbases of the blocks prevent the water from scouring the aggregate frombeneath the blocks, and the close spacing of the blocks preventsdisplacement of the blocks by water scouring between them.

I claim:

1. A revetment block with a triangular prismatic base and an upperangular apex, the base having a notch in one side to receive theextremity of an angular corner of the base of a similar block toposition and interengage blocks in adjacentcourses for holding them inpredetermined position.

2. A revetment comprising a layer of aggregate covering a surface to beprotected from water action; a plurality of concrete blocks supported bythe layer and spaced with open joints no wider than the particle size ofthe aggregate; and each block comprising an equilateral right angledprismatic base of a height which allows opposed bottom side edges ofadjacent blocks to shift relatively, either upwardly or downwardlywithout exposing the layer beneath; and each block having a pyramidalsuperstructure rising centrally from its base to break up said wateraction.

3. A revetment in accordance with claim 2 in which the angular relationof the faces of the pyramidal superstructure is that they areequilateral and make an angle of ninety degrees or more at the apex withthe opposite faces or edges so that the force of an impact on the facewill have a direction to fall with the base of the unit and will nottend to overturn it.

LEROY F. HARZA.

